1. Field of the Invention
The present invention relates to a display device, and more particularly, a display device which facilitates to prevent an abnormal display during a driving mode conversion, an abnormal signal input, and a no-signal input, and a method for driving the same.
2. Discussion of the Related Art
According to a development in various mobile electronic equipments such as mobile terminal and notebook computer, there is the increasing demand for an applicable flat panel display device.
The flat panel display device may include a liquid crystal display device (LCD), a plasma display panel (PDP), a field emission display device (FED), an organic light-emitting diode display device (OLED), and etc.
Recently, a user is highly interested in OLED owing to various advantages. For example, the OLED emits light in itself without using an additional light source, and the OLED has great brightness, good contrast ratio, wide viewing angle, and rapid response speed.
Depending on a driving method, the OLED may be largely classified into a passive matrix type and an active matrix type.
In case of the passive matrix type, pixels are arranged in a matrix configuration without an additional thin film transistor (hereinafter, referred to as ‘TFT’). The respective pixels are sequentially driven according to sequentially-driven scanning lines. Thus, the increased number of lines requires higher voltage supply and instantaneous current application, whereby power consumption is increased, and resolution is limited.
In case of the active matrix type, pixels are arranged in a matrix configuration, and TFTs are respectively formed in the pixels. The respective pixels are driven by switching the TFT and charging a voltage of a storage capacitor (Cst). In comparison to the passive matrix type, the active matrix type has relatively-low power consumption and relatively-high resolution. Thus, the active matrix type OLED is suitable for the display device requiring high resolution and large-sized screen.
Hereinafter, the active matrix type OLED will be briefly referred to as the OLED. Among the various flat display devices, the OLED will be explained in comparison to the LCD device.
The LCD device according to the related art displays an image by controlling light transmittance pixel-by-pixel depending on an input video signal. For this, the LCD device comprises a liquid crystal panel with plural pixels (liquid crystal cells) arranged in a matrix configuration; a backlight unit for supplying light to the liquid crystal panel; and a driving circuit for driving the liquid crystal panel and the backlight unit.
The LCD device according to the related art sequentially supplies input video to the liquid crystal panel line-by-line, and supplies light emitted from a light source to the liquid crystal panel, thereby displaying image.
A pixel voltage is made by a common voltage and a data voltage supplied to each pixel. Then, transmittance of light emitted from the backlight unit can be controlled by aligning liquid crystal molecules of a liquid crystal layer depending on the pixel voltage, to thereby realize the image.
At this time, a lower polarizing sheet (polarizing plate) is provided at the lower side of the liquid crystal panel, wherein the lower polarizing sheet polarizes the light supplied from the backlight unit. An upper polarizing sheet (polarizing plate) is provided at the upper side of the liquid crystal panel, wherein the upper polarizing sheet polarizes the light emitted from the liquid crystal layer.
FIG. 1 illustrates a mode conversion method of an LCD device according to the related art.
In an LCD device according to the related art, as shown in FIG. 1, a system main power is turned-on so as to drive a normal mode (input image driving mode) for displaying an image on a liquid crystal panel according to input video data.
After that, a low voltage differential signal (LVDS) is generated by reading EEP data from an internal memory, wherein the EEP data is provided for driving the liquid crystal panel and driving circuit.
By the use of input video data from the external, respective pixels of the liquid crystal panel are driven to operate a light source of a backlight unit, to thereby supply the light to the liquid crystal panel.
Through these steps, the normal mode is driven to thereby display the image on the liquid crystal panel.
For the mode conversion of the related art LCD device from the normal mode to a sleep mode (power save mode), it firstly needs to enter a stand-by mode. Then, the light source of the backlight unit is turned-off so as to stop the light supply to the liquid crystal panel.
After that, the video data supply to the liquid crystal panel is stopped following stopping the generation of LVDS, whereby the system main power is turned-off.
Accordingly, the image is not displayed on the liquid crystal panel by the mode conversion from the normal mode to the sleep mode through the above steps.
On the mode conversion from the normal mode to the sleep mode, black video data is supplied to the liquid crystal panel, to thereby display a black image on the liquid crystal panel. Prior to the video data supply to the liquid crystal panel, the driving of the backlight unit is turned-off so as to stop the light emission from the light source, thereby preventing the image from being abnormally displayed for the mode conversion.
In the related art LCD device, the mode conversion from the normal mode to the sleep mode is made by the driving method shown in FIG. 1, and the display conversion is smoothly performed by the mode conversion from the sleep mode to the normal mode.
If the video data is normally inputted for a frame period, the backlight unit is turned-off to stop the light supply to the liquid crystal panel. Thus, even though the abnormal video data is supplied to the liquid crystal panel, the abnormal image is not displayed on the liquid crystal panel. That is, when the abnormal video data is supplied to the liquid crystal panel, the black image is displayed on the liquid crystal panel.
Unlike the LCD device, the OLED can emit light in itself so that the OLED has no backlight unit therein.
In case of the OLED, each pixel is driven according to the video data supplied to a display panel, to thereby display the image. Thus, if there is the mode conversion, the abnormal image may be displayed on the display panel.
FIGS. 2 and 3 illustrate the problem of abnormal display by the mode conversion or abnormal-signal input in the related art OLED.
Referring to FIGS. 2 and 3, an input signal (video data and driving signal) should be monitored so as to make the smooth mode conversion of the system, to thereby prevent the abnormal display for the mode conversion.
In order to prevent the abnormal image display, it is necessary to detect the abnormal signal input and no-signal input, and to process the detected signal.
However, the related art OLED does not show the structure or method capable of preventing the abnormal display for the mode conversion, abnormal signal input, and no-signal input.
Even though the abnormal video data is supplied from the external to the related art OLED, it is not checked whether or not the input data is abnormal, whereby the abnormal video data may be displayed on the display panel.
Even though the abnormal signal is supplied to the display panel 10, or the supply of the video data is stopped for a frame period, it is not checked so that the abnormal display may be shown on the display panel.
On the abnormal signal input or mode conversion, plural gate lines may be turned-on due to errors in gate control signals. Thus, the display panel 10 may be damaged to thereby shorten the lifespan of the display panel 10.
In order to overcome these problems, the video data corresponding to the frame for the mode conversion is not displayed for the mode conversion. If the video data is inputted abnormally, that is, in case of the no-signal input, it needs an additional display mode capable of substituting the no-signal input.
However, in case of the related art OLED, there is no additional display mode handling the problems of mode conversion, abnormal signal input, and no-signal input. Also, the related art OLED does not include the structure and method capable of preventing the abnormal display on the mode conversion or abnormal signal input.